refactor: remove visitor pattern #37

2026-01-17T20:45:13Z

mvhutz commented

2026-01-17 20:45:13 +00:00

Description

The codebase previously used the visitor pattern for traversing lambda calculus expressions.
This was a hold-over from avoiding the Go-idiomatic way of handling types.
This PR removes the visitor pattern in favor of direct method implementations.

Remove Visitor interface from expression.go.
Remove Accept methods from Abstraction, Application, and Variable.
Remove Accept from Expression interface.
Delete stringify.go and move String() logic directly into each type.
Add compile-time interface checks (var _ Expression = (*Type)(nil)).
Update expr.Expression to embed fmt.Stringer instead of declaring String() string.

Decisions

Moved String() implementations directly into each expression type rather than using a separate recursive function, as each type's string representation is simple enough to be self-contained.

Benefits

Simpler, more idiomatic Go code using type methods instead of visitor pattern.
Reduced indirection and fewer files to maintain.
Compile-time interface satisfaction checks catch implementation errors early.

Checklist

Code follows conventional commit format.
Branch follows naming convention (<type>/<description>).
Tests pass (if applicable).
Documentation updated (if applicable).

Closes #36

## Description The codebase previously used the visitor pattern for traversing lambda calculus expressions. This was a hold-over from avoiding the Go-idiomatic way of handling types. This PR removes the visitor pattern in favor of direct method implementations. - Remove `Visitor` interface from `expression.go`. - Remove `Accept` methods from `Abstraction`, `Application`, and `Variable`. - Remove `Accept` from `Expression` interface. - Delete `stringify.go` and move `String()` logic directly into each type. - Add compile-time interface checks (`var _ Expression = (*Type)(nil)`). - Update `expr.Expression` to embed `fmt.Stringer` instead of declaring `String() string`. ### Decisions - Moved `String()` implementations directly into each expression type rather than using a separate recursive function, as each type's string representation is simple enough to be self-contained. ## Benefits - Simpler, more idiomatic Go code using type methods instead of visitor pattern. - Reduced indirection and fewer files to maintain. - Compile-time interface satisfaction checks catch implementation errors early. ## Checklist - [x] Code follows conventional commit format. - [x] Branch follows naming convention (`<type>/<description>`). - [x] Tests pass (if applicable). - [ ] Documentation updated (if applicable). Closes #36

mvhutz added 2 commits 2026-01-17 20:45:13 +00:00

refactor: replace visitor pattern with type-switch recursion dbb988b633

Closes #36

feat: fmt.Stringer 3ef27bc28a

mvhutz merged commit c2aa77cb92 into main

2026-01-17 20:46:07 +00:00

mvhutz deleted branch refactor/no-visitor-pattern

2026-01-17 20:46:07 +00:00

mvhutz referenced this issue from a commit

2026-01-17 20:46:09 +00:00

refactor: remove visitor pattern (#37)

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Reference: mvhutz/lambda#37